1. Field of the Invention
The present invention relates to a resource allocating method for a base station to allocate a necessary resource to communication with a mobile station, and to a base station, a mobile station, and a radio packet communication system to which the resource allocating method is applied.
2. Related Background Art
In a radio packet communication system such as a mobile communication system, on the occasion of implementing packet communication between a mobile station and a base station, the base station allocates a resource to communication with the mobile station.
One of the conventionally known resource allocating methods is, for example, the IEEE802.11b system defining the standards for radio data communication (cf. Nonpatent Document 1 below). In this system, packet communication is carried out as follows. When a terminal has packets to be transmitted, it checks a state of a channel through the use of the carrier-sense function. When a channel is idle (unused) on that occasion, the terminal starts transmitting the packets after a lapse of a predetermined time (IFS: Interframe Space). If the channel is busy (in use) on the occasion of checking the state of the channel through the use of the carrier-sense function, the terminal waits before the channel becomes idle. With detection of an idle state of the channel, the terminal starts transmitting the packets after a lapse of the IFS. If on this occasion packets have a plurality of priority classes, IFSs are determined according to the respective priority classes. As the IFSs, there are three values of SIFS (Short IFS), PIFS (PCF IFS), and DIFS (DCF IFS) in order from the shortest. For transmitting a packet with a high priority level, an IFS of a short value is used to permit the packet to occupy the channel at earlier timing than a packet with a lower priority level, whereby the packet can be preferentially transmitted.
There is also a conventionally known method of controlling the transmit power in uplinks in the W-CDMA system (cf. Patent Document 1 below). Attenuation of a radio wave increases with increasing distance, so as to pose the so-called “near-far problem” that communication becomes hard with a mobile station distant from the base station. In order to solve the “near-far problem,” the W-CDMA system adopts such control on the transmit power as to equalize SIRs (Signal to Interference Ratios) of received data from all the mobile stations. Specifically, the base station calculates an SIR from a received pilot signal from a mobile station and compares the calculated SIR with a required SIR preliminarily set. Then the base station transmits a signal to control the transmit power, to the mobile station, in order to make the SIR calculated from the pilot signal, agree with the required SIR.
[Patent Document 1]
Japanese Patent Application Laid-Open No. 2002-16545
[Nonpatent Document 1]
IEEE802.11b 1999 Edition, pp. 74-76